1. Field of the Disclosure
Aspects of the disclosure generally are related to an apparatus and a method for generating an interference fringe pattern. More specifically, the disclosure is related to a holographic microscope.
2. Description of the Related Art
For real-time dual-wavelength imaging, Kühn et al. disclosed a technique to perform two-wavelength digital holographic microscopy measurements with a single hologram acquisition (Jonas Kühn, Tristan Colomb, Frédéric Montfort, Florian Charrière, Yves Emery, Etienne Cuche, Pierre Marquet, and Christian Depeursinge, Optics Express, Vol. 15, No. 12, pp. 7231-7242 (2007)).
Since two semiconductor laser diodes at λ1=679.57 nm and λ2=759.91 nm are used for obtaining a two-wavelength hologram, the spatial frequencies of each wavelength in the Fourier spectrum of the hologram is filtered (selected) separately.
The reason why Kühn et al. uses two laser sources to obtain the two-wavelength hologram is that they can create a synthetic beat wavelength which is much longer than either of the laser wavelengths. The range of the measurable sample depth is limited by the light wavelength used. Therefore, using the synthetic beat wavelength may increase the range of the sample depth measured.